1. Field of the Invention
The present invention relates to a switching power supply controller and a switching power supply.
2. Related Background Art
A switching power supply has such properties as small size, light weight, and high efficiency and is commonly used as a power supply for microcomputers as incorporated in various devices, personal computers, and so on. These personal computers and others are progressively advancing toward lower voltage and higher processing speed, while increasing the consumption current more and more. In the switching power supply, therefore, the load current suddenly increases or decreases according to the processing load in the personal computers and others. The switching power supply possesses the property of capability of readily adapting to a wide input voltage range and is also utilized as a power supply applicable in several countries in the world or as a power supply with a wide specification setting of input voltage. The switching power supply needs to insure the stable output voltage against change of the load current and input voltage as described above. Furthermore, even if the output voltage is in a transient response state to a sudden change of the load current or the input voltage, the switching power supply must recover quickly into a stable state.
For this reason, the switching power supply is equipped with a controller such as a controller IC [Integrated Circuit] or the like of a digital control system, and this controller quickly turns switching elements such as FETs [Field Effect Transistors] or the like on and off (cf. “The Fundamentals of Switched-Mode Converters,” coauthored by Kousuke Harada, Tamotsu Ninomiya, and Bunken Ko and published by CORONA PUBLISHING CO., LTD.). The controller adopts the feedback control based on voltage mode control or current mode control to generate a PWM [Pulse Width Modulation] signal for turning the switching elements on and off on the basis of the output voltage or the like of the switching power supply. Where the gain of this controller is denoted by Gc, the gain of the entire system including the switching power supply is given by the product of the input voltage VI and the gain Gc.